1. Field of the Invention
The invention relates in general to transportation apparatus, and more specifically to an escalator or a moving walk having means for controlling its deceleration rate during a stop.
2. Description of the Prior Art
Copending application Ser. No. 605,041, filed Apr. 30, 1984, discloses transportation apparatus, such as an escalator, which is feedback controlled to stop the apparatus according to a predetermined speed pattern. An AC component is added to a unidirectional signal responsive to actual speed, to modulate the brake current for smoother and more accurate control.
Copending application Ser. No. 644,754, filed Aug. 27, 1984, improves upon the transportation apparatus disclosed in application Ser. No. 605,041. The improvements relate to causing the speed pattern to track the actual speed of the apparatus, without exceeding it, so their values are relatively close to one another at the time deceleration is initiated. Also, the speed pattern ramp is delayed until the actual speed of the transportation apparatus drops to the starting value of the speed pattern. The arrangements of the copending applications, which are both assigned to the same assignee as the present application, perform well when applied to an escalator having a single drive unit. In an application of the teachings of the copending applications to an escalator having two drive units, one servo loop was used to drive the brakes of the two drives in parallel, with tachometer feedback coming from one of the drives. The results were not consistent, and the actual speed of the escalator varied significantly from the desired speed established by the slope of the slowdown portion of the speed pattern signal. U.S. Pat. No. 3,707,220 describes an escalator of the type which may have more than one drive unit, with the number of drive units being dictated by the rise of the escalator.
Thus, it would be desirable to provide a new and improved braking arrangement for controlling the slowdown of transportation apparatus, such as an escalator, after its drive unit, or drive units, are disconnected from the power source, with the new and improved braking arrangement being equally suitable for single or multi-drive escalators or moving walks.